The nature of calcium regulation in bone cells will be studied with specific emphasis on the interrelationships of calcium, cyclic nucleotides and calmodulin. Enriched populations of osteoclastic and osteoblastic cells will be obtained by sequential collagenase digestions of fetal and newborn rat calvaria followed by flow cytometry studies. Cyclic AMP and GMP will be measured by radioimmunoassay. Calcium transport will be measured in intact cells and plasma membrane vesicles with 45Ca. The effects of bone resorptive agents and inhibitors of resorption on cyclic GMP levels in characterized cell populations will be studied as well as the effects of cyclic GMP on calcium transport. Calmodulin activity in bone cells will be assessed by radioimmunoassay and the effects of anti-calmodulin drugs on cyclic AMP, cyclic GMP regulation and calcium transport will be studied. The role of calmodulin in regulating adenylate/guanylate cyclase and calcium transport will be studied directly in enriched membrane fractions. The information obtained in these studies should further elucidate the role of calcium and cyclic nucleotides in the control of bone metabolism. The studies should also provide a clearer understanding of the biochemical processes involved in control of bone metabolism and could theoretically lead to a more rationale approach to the treatment of metabolic bone disease.